Fuel cell

ABSTRACT

A fuel cell is provided which can enhance the CO resistance to thereby improve the voltage characteristics thereof. A fuel cell includes an electrolyte layer, a first electrode provided on one surface of the electrolyte layer, and a second electrode provided on the other surface of the electrolyte layer. In this fuel cell, a reaction fluid to be supplied to the first electrode contains carbon monoxide or carbon monoxide is generated from a reaction fluid having been supplied to the first electrode. The first electrode of the fuel cell includes a first catalyst material (Pt) having a function of extracting an electron from the reaction fluid, a second catalyst material (WAu) having a function of reducing the activation energy for conversion of carbon monoxide to carbon dioxide, and an oxygen-supplying material (Ru) supplying oxygen.

RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.11/524,527, filed on Sep. 21, 2006, now U.S. Pat. No. 7,700,220,claiming priority of Japanese Patent Application Nos. 2005-274234, filedon Sep. 21, 2005, and 2006-230109, filed on Aug. 28, 2006, the entirecontents of each of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell, and in particular, to afuel cell having high CO resistance.

2. Description of the Related Art

In this age, the new technologies that have evolved, such as IT andbiotechnology, have had a global impact. Even in such circumstances,however, the energy industry remains one of the largest basicindustries. In recent years, as environmental awareness includingprevention of global warming has grown, expectations regarding theintroduction of a so-called new energy have increased. This new energyhas advantages in terms of reduction in power transmission losses andsecurity of power supply, in addition to environmental friendliness,given that the energy can be produced in dispersed sites close to theelectrical power consumers. Furthermore, as a secondary effect, it isexpected that new related industries will be created through thedevelopment of this new energy. Efforts to develop this new energy beganin earnest, triggered by the oil crisis of approximately 30 years ago.At present, the following types of new energy are still at thedevelopment stage, but are moving toward practical use: reproducibleenergy produced by solar photovoltaic power generation or the like,recycled energy produced by waste power generation or the like, highefficiency energy produced by a fuel cell or the like, and energy in newfields, as typified by clean energy vehicles.

Among these examples, the energy produced by a fuel cell is one of thetypes receiving the most attention from industry. A fuel cell generateselectricity and heat simultaneously through chemical reaction of oxygenin an atmosphere with hydrogen, produced through the reaction of watervapor with natural gas, methanol, or the like. A fuel cell produces onlywater as a by-product of power generation. In addition to this, highefficiency is obtained even in a low power output range, and theelectrical power generation is not affected by weather, and therefore,is stable. In particular, the polymer electrolyte fuel cell has receivedsignificant attention as one of the next-generation standard powersources for applications such as use in vehicles, mobile use, andstationary use such as in housing. The following technologies have beendeveloped for commercialization based on the polymer electrolyte fuelcell: a technology employing a small size catalyst of nanometer order,in order to improve power generation performance (see Published Japanesetranslation of PCT international application No. 2005-515063); and atechnology in which gold nanoparticles are added to a catalyst in orderto improve CO (carbon monoxide) resistance (see Koji Matsuoka, KoheiMiyazaki, Yasutoshi Iriyama, Takeshi Abe, and Zempachi Ogumi, “MethanolOxidization Characteristics of Pt—Ru Catalyst Supported on GoldUltra-fine Particles”, Proceedings of the 45th cell forum, the Committeeof Battery Technology, the Electrochemical Society of Japan, (11/27Heisei 16), pp. 620-621, and Kohei Miyazaki, Koji Matsuoka, YasutoshiIriyama, Takeshi Abe, and Zempachi Ogumi, “Electro-oxidation of Methanolon Gold Nanoparticles Supported on Pt/MoO_(x)/C”, Journal of TheElectrochemical Society, 152(9) A1870-A1873 (2005).

In the case where hydrogen is produced through the reaction of naturalgas or methanol with water vapor as mentioned above, ideally, 80% ofhydrogen (H₂) and 20% of carbon dioxide (CO₂) are supplied to a fuelcell through the reaction represented by the chemical equations (1) and(2). However, since carbon monoxide (CO) generated during the processesrepresented by the chemical equations (1) and (2) cannot be fullyeliminated, CO in an amount of several ppm to several tens of ppm entersthe anode of the fuel cell.CH₄+H₂O→3H₂+CO  (1)CO+H₂O→CO₂+H₂  (2)

Furthermore, in the case where an aqueous solution containing methanol(organic fuel) is supplied to a fuel cell, the reaction represented bythe chemical equation (3) occurs on the anode side. However, CO which isnot converted into carbon dioxide during the reaction process remains atthe anode.CH₃OH+H₂O→6H⁺+6e ⁻+CO₂  (3)

Hence, in a catalyst layer for the anode of a fuel cell which generateselectrical power by means of organic fuel or reformed gas obtainedthrough reforming reaction (transformation reaction), a catalyst such asplatinum (Pt) which has a function of converting H₂ to protons (H⁺) hasusually been employed. In addition to platinum, a PtRu catalyst has alsobeen employed to which ruthenium (Ru) is added in order to prevent thereduction of catalytic activity caused by CO poisoning of Pt. Materialssuch as ruthenium (Ru) have properties that promote the conversion ofthe CO that sticks to Pt to CO₂. Furthermore, a technology has beenreported which improves CO resistance by mixing a catalyst composed ofPt and Ru or Pt and molybdenum (Mo) with gold nanoparticles. However,this technology is still in the research stage. Although fuel cellsappear on the verge of becoming genuinely widespread, it has been foundthat, at present, the CO resistance at the anode is not sufficient.

SUMMARY OF THE INVENTION

The present invention has been developed in view of the foregoingproblems. It is thus a general purpose of the present invention toprovide a technology that enhances the CO resistance of a catalyst tothereby improve the characteristics of fuel cells.

In order to achieve the foregoing object, one embodiment of the presentinvention relates to a fuel cell which includes an electrolyte layer, afirst electrode provided on one surface of the electrolyte layer, and asecond electrode provided on the other surface of the electrolyte layer,and in which a reaction fluid to be supplied to the first electrodecontains carbon monoxide or carbon monoxide is generated from a reactionfluid having been supplied to the first electrode. In this fuel cell,the first electrode includes a first catalyst material having a functionof extracting an electron from the reaction fluid, a second catalystmaterial having a function of reducing activation energy for conversionof the carbon monoxide to carbon dioxide, and an oxygen-supplyingmaterial which supplies oxygen.

In the present specification, any fuel and oxidant required for a fuelcell to generate power are collectively called the reaction fluid.Furthermore, activation energy is the minimum energy required for thereactants to initiate a reaction in order for a chemical reaction toproceed. Thus, among the reactant molecules, molecules having energylarger than the activation energy can be converted to product moleculesthrough recombination of bonds between atoms.

Examples of the fuel cell in which a reaction fluid to be supplied tothe first electrode contains carbon monoxide (CO) include a fuel cellwhich employs reformed gas supplied thereto as fuel. In this instance,the reformed gas is formed by reforming hydrocarbon-based raw fuel suchas LPG or city gas by means of a reforming apparatus. However, thepresent invention is not limited thereto. For example, when air isemployed as oxidant, this air may contain CO. Furthermore, examples of afuel cell in which carbon monoxide is generated from a reaction fluidhaving been supplied to the first electrode include a liquid fuel directsupply fuel cell. In this fuel cell, liquid fuel such as an aqueoussolution of methanol is directly supplied to the fuel cell, and thus COmay be generated as an intermediate product of the anode reaction.

In the present invention, by employing the above configuration, evenwhen CO sticks to the first catalyst material, a state in which CO iseasily converted to CO₂ is maintained by means of the second catalystmaterial. Therefore, by supplying oxygen (O) from the oxygen-supplyingmaterial, the reduction in the ability of the first catalyst materialcaused by CO poisoning can be suppressed (and CO resistance is thereforeimproved) to thereby improve the voltage characteristics of the fuelcell.

Furthermore, another embodiment of the present invention relates to acatalyst employed in a fuel cell. The catalyst includes a first catalystmaterial having a function of extracting an electron from a reactionfluid, a second catalyst material having a function of reducingactivation energy for conversion of carbon monoxide to carbon dioxide,and an oxygen-supplying material which supplies oxygen. According tothis catalyst for a fuel cell, even when CO sticks to the first catalystmaterial, a state in which CO is easily converted to CO₂ is maintainedby means of the second catalyst material. Therefore, by supplying oxygen(O) from the oxygen-supplying material, CO resistance can be improved,whereby the durability of a fuel cell employing this catalyst can alsobe improved.

Moreover, the second catalyst material may contain gold and a transitionmetal selected from group 3 to group 11. Preferably, the particlediameter distribution of the gold has a peak within the range of from 1nm to 5 nm. Furthermore, preferably, the transition metal has anoxidation-reduction potential within a range in which a standardelectrode potential thereof with respect to a standard hydrogenelectrode is −0.25 V or more and 0.25 V or less.

The gold particles having the peak of the particle diameter distributionwithin the range of from 1 nm to 5 nm, or so-called gold nanoparticles,exhibit outstanding CO oxidizing ability. Furthermore, the CO oxidizingability of the gold nanoparticles can be enhanced by employing, as amaterial supporting the gold nanoparticles, a transition metal selectedfrom group 3 to group 11, particularly a transition metal having anoxidation-reduction potential within a range in which a standardelectrode potential thereof with respect to a standard hydrogenelectrode is −0.25 V or more and 0.25 V or less.

Moreover, desirably, the oxygen-supplying material contains at least oneselected from the group consisting of magnesium, aluminum, vanadium,chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium,molybdenum, ruthenium, rhodium, palladium, tin, tungsten, and iridium.When importance is placed on the oxygen supplying ability of theoxygen-supplying material, ruthenium is the optimum choice. However,when chromium, tin, or tungsten is employed as the oxygen-supplyingmaterial, a common material can be employed for the oxygen-supplyingmaterial and the material supporting the gold nanoparticles, and thusoverall costs can be reduced. In addition to the above, it isconceivable that a transition element (transition metal) selected fromgroup 3 to group 11 of the periodic table (from group 3A to group 7A,group 8, and group 1B) can be primarily employed.

Still another embodiment of the present invention relates to a fuel cellwherein the first electrode has a first region contacting a reactionfluid having a lower carbon monoxide concentration and a second regioncontacting a reaction fluid having a higher carbon monoxideconcentration, and wherein the concentration of the second catalystmaterial in the first region is lower than that in the second region.Yet another embodiment of the present invention relates to a fuel cellwherein the first electrode has a first region contacting a reactionfluid having a lower carbon monoxide concentration and a second regioncontacting a reaction fluid having a higher carbon monoxideconcentration, and wherein the concentration of the oxygen-supplyingmaterial in the first region is lower than that in the second region.

The relative concentration of carbon monoxide contained in the reactionfluid is higher in a region close to a discharging portion from which areaction fluid not reacted at the first electrode is discharged than ina region close to an introduction portion for supplying the reactionfluid to the first electrode. Therefore, in the region contacting afluid having higher relative carbon monoxide concentration (the secondregion), CO can be effectively converted to CO₂ by increasing theconcentration of the second catalyst material or the concentration ofthe oxygen-supplying material so as to increase the number of reactionsites where CO is brought into close proximity of O.

It is to be noted that any arbitrary combination or rearrangement of theabove-described structural components and so forth are all effective asand encompassed by the present embodiments.

Moreover, this summary of the invention does not necessarily describeall necessary features so that the invention may also be sub-combinationof these described features.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 is a schematic diagram illustrating the configuration of a fuelcell according to the present invention;

FIG. 2 is a schematic diagram illustrating the configuration of adomestic-use fuel cell co-generation system employing the fuel cellaccording to the present invention;

FIG. 3 is a schematic diagram illustrating the configuration of the fuelcell of the present invention employed in a first embodiment;

FIG. 4 is a graph showing the current-voltage characteristics of thefuel cell according to Examples 1 and 2 of the present invention;

FIG. 5 is a schematic diagram illustrating the configuration of the fuelcell according to Example 3 of the present invention;

FIG. 6 is a schematic diagram illustrating the configuration of amobile-use fuel cell system employing the fuel cell according to thepresent invention;

FIG. 7 is a schematic diagram illustrating the configuration of the fuelcell according to Reference Example of the present invention; and

FIG. 8 is a schematic diagram illustrating the configuration of the fuelcell according to Example 6 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention.

Hereinafter, a fuel cell 10 of the present invention will be describedin detail with reference to the drawings. As shown in FIG. 1, the fuelcell 10 of the present invention is provided with: a positive electrode(cathode) 14 which is provided on one surface of a solid polymermembrane 12 and at which a reduction reaction occurs by means of anoxygen (O) source such as oxygen in air; and a negative electrode(anode) 22 which is provided on the other surface of the solid polymermembrane 12 and at which an oxidization reaction occurs by means of ahydrogen (H) source such as pure hydrogen, reformed gas, or methanol.Generally, a proton exchange membrane is widely employed for the solidpolymer membrane 12. The H-source donates an electron at the anode 22 toform a proton (H⁺), and the thus-formed proton moves to the cathode 14through the solid polymer membrane 12 and reacts with the O-source whichhas received an electron at the cathode 14. Hence, electrical power canbe supplied to the outside of the fuel cell 10, and water (H₂O) isgenerated at the cathode 14. Furthermore, since the series of reactionsis exothermic, the fuel cell 10 can be used as a co-generation systemwhich draws and utilizes heat as well as electricity, and thus theoverall energy efficiency of the fuel cell is improved.

Next, a description will be given of a specific embodiment of the fuelcell 10 having the above basic configuration.

First Embodiment

In this embodiment, with reference to FIG. 2, a description will begiven of a fuel cell 110 employed in a domestic-use fuel cellco-generation system 100. The domestic-use fuel cell co-generationsystem 100 includes: a reforming apparatus which reforms raw fuel(hydrocarbon-based fuel) such as LPG or city gas and generates reformedgas containing hydrogen (fuel) in an amount of about 80%; a fuel cell110 which generates electrical power using the reformed gas suppliedfrom the reforming apparatus and oxygen (oxidant) in air; and a hotwater storage apparatus which recovers and stores heat generated in thereforming apparatus and the fuel cell 110 in the form of hot water(water of 40° C. or higher). Thus, this system has both a powergeneration function and a hot water supplying function.

Normally, as safety measures in case of a gas leak, an odor is added, byuse of a sulfide, to the raw fuel, such as LPG or city gas, supplied tohomes. However, the sulfide causes catalyst deterioration in thereforming apparatus. Thus, the sulfide in the raw fuel is first removedin the reforming apparatus by means of a desulfurizer 152. The raw fuel,having been desulfurized by means of the desulfurizer 152, is then mixedwith water vapor. The mixture is subjected to water vapor reforming bymeans of a reformer 154 and is introduced to a transformer 156. Areformed gas containing about 80% hydrogen (H₂), about 20% carbondioxide (CO₂), and 1% or less carbon monoxide (CO) is generated by meansof the transformer 156. However, in the present system 100, the reformedgas is supplied to the fuel cell 110 operated at low temperatures (100°C. or lower) where the cell is likely to be affected by CO, and thus thereformed gas is mixed with oxygen to selectively oxidize CO by means ofa CO remover 158. The use of the CO remover 158 means that the COconcentration in the reformed gas can be reduced to 10 ppm or less.

The reforming apparatus includes at least the reformer 154 and thetransformer 156. When the gas supplied to homes is employed as raw fuel,as in the present system 100, the reforming apparatus further includesthe desulfurizer 152. When a low temperature type fuel cell 110 such asa polymer electrolyte fuel cell is employed as the fuel cell 110, thereforming apparatus further includes the CO remover 158.

Since the water vapor reforming is an endothermic reaction, a burner 160is provided in the reformer 154. At startup of the reforming apparatus,the raw fuel is also supplied to the burner 160 to raise the temperatureof the reformer 154. Once the present system 100 is operating stably,the supply of raw fuel to the burner 160 is terminated and unreactedfuel discharged from the fuel cell 110 is supplied to the burner 160,whereby heat is supplied to the reformer 154. Since the exhaust gashaving supplied heat to the reformer 154 through the burner 160 stillretains a large amount of heat, the exhaust gas is subjected to heatexchange with water in a hot water storage tank 162 by means of heatexchangers HEX01 and HEX02. Then, this water, subjected to heat exchange(HEX03) with an exhaust gas from the cathode 114 of the fuel cell 110,is further subjected to heat exchange (HEX04) with an exhaust gas froman anode 122, and then returns to the hot water storage tank 162. Inorder to utilize the temperature of the water (hot water) having passedthrough the heat exchanger HEX04 for heating or cooling a cathode-sidehumidification tank 166, a branched tube 168 is provided in a water tube164 passing through the heat exchangers HEX01 to HEX04. At the time of,for example, startup of the present system 100, the temperature of thecathode-side humidification tank 166 is low. In such a case, the waterpasses through the heat exchanger HEX04 and then the branched tube 168.Then, at a heat exchanger HEX05, the water supplies heat to thecathode-side humidification tank 166 and returns to the hot waterstorage tank 162.

This cathode-side humidification tank 166 also serves as a cooling watertank, and the water in this humidification tank 166 cools the fuel cell110 and returns to the tank 166. As described above, the temperature ofthe fuel cell 100 is low at the time of, for example, startup of thepresent system 100, and thus the fuel cell 110 can be warmed bysupplying thereto the cooling water warmed by the heat exchanger HEX05.Furthermore, a cooling water passage 170 through which the cooling waterflows is connected to a heat exchanger HEX06 provided in an anode-sidehumidification tank 172. The cooling water also plays a role in matchingapproximately the temperature of the cathode-side humidification tank166 with the temperature of the anode-side humidification tank 172.

The reformed gas from the reforming apparatus is humidified (bubbled, inthe case of the present system 100) in this anode-side humidificationtank 172 and is supplied to the anode 122. The unreacted fuel notinvolved in power generation at the anode 122 is discharged from thefuel cell 110 and is supplied to the burner 160. Normally, the fuel cell110 is operated so as to generate electrical power at temperatures inthe range of 70 to 80° C. Since the exhaust gas discharged from the fuelcell 110 has a temperature of about 80° C., the exhaust gas is subjectedto heat exchange in the heat exchanger HEX04 as described above.Subsequently, in a heat exchanger HEX07, the exhaust gas raises thetemperature of the water supplied to the cathode-side humidificationtank 166 and the anode-side humidification tank 172 and is then suppliedto the burner 160.

It is preferable that the water supplied to the cathode-sidehumidification tank 166 and the anode-side humidification tank 172 isclean water having low electrical conductivity and containing only asmall amount of organic materials. Therefore, water supplied from theregional waterworks is subjected to water treatment by use of a reverseosmosis membrane and ion-exchange resin by means of a water treatmentapparatus 174, and this treated water is employed as the water to besupplied to the humidification tanks. Furthermore, the water subjectedto water treatment is also employed for water vapor reforming by meansof the reformer 154. The water from waterworks is also supplied to thehot water storage tank 162. At this time, the water from waterworks issupplied to this storage tank 162 from a lower portion thereof. Thewater tube 164 draws low temperature water from the lower portion ofthis storage tank 162 and returns water subjected to heat exchange ineach of the heat exchangers to an upper portion of the storage tank 162.

HEX10 is a total enthalpy heat exchanger. The exhaust gas containingunreacted oxygen not involved in power generation at the cathode 114contains product water generated through heat of about 80° C. andvarious reactions. Thus, in the total enthalpy heat exchanger HEX10, theexhaust gas supplies heat and moisture to air supplied to the cathode114. The air to be supplied to the cathode 114 is humidified (bubbled,in the case of the present system 100) in the cathode-sidehumidification tank 166 and is then supplied to the cathode 114.Furthermore, the exhaust gas having supplied heat and moisture in thetotal enthalpy heat exchanger HEX10 is further subjected to heatexchange with water in the heat exchanger HEX03 and is discharged tooutside the present system 100.

The fuel cell 110 of this embodiment is provided with diffusion layers120 and 128 in order to uniformly supply the reformed gas to the cathode114 and the anode 122 and in order to smoothly discharge product waterfrom the cathode 114 and water condensed in the cathode 114 and theanode 122. The diffusion layers are prepared using carbon paper, carbonwoven fabric, or carbon non-woven fabric as a substrate and by applyingto the substrate a viscous carbon paste formed mainly of carbon black.In consideration of efficient productivity, the same carbon paper isemployed as the substrate for both the diffusion layers 120 and 128, anddifferent diffusion layer pastes, i.e., a cathode-side paste and ananode-side paste, are applied to the respective substrates, as shown inFIG. 3. More specifically, a cathode-side packed layer 116 is preparedby applying a cathode-side diffusion layer paste to a cathode-sidesubstrate 118, drying the paste, and subjecting it to heat treatment. Inthis case, the packed layer 116 is prepared such that the waterrepellency (provided by the content of fluororesin) is lower than thaton the anode side. Furthermore, an anode-side packed layer 124 isprepared by applying an anode-side diffusion layer paste to ananode-side substrate 126, drying the paste, and subjecting it to heattreatment. In this case, the packed layer 124 is prepared such that thewater repellency (provided by the content of fluororesin) is higher thanthat on the cathode side.

However, general fluororesin (hereinafter referred to as high molecularweight fluororesin) has good binding properties. Therefore, when a largeamount of high molecular weight fluororesin is added to the diffusionlayer paste, the viscosity increases due to mixing and application, andthe fluororesin aggregates as clusters. Therefore, a difficulty arisesin the application step. In view of this difficulty, low molecularweight fluororesin, which has an average molecular weight smaller thanthat of the high molecular weight fluororesin and has very poor bindingproperties, is also employed. In this case, the low molecular weightfluororesin is responsible for water repellency, and the high molecularweight fluororesin is responsible for binding properties, whereby eachof the diffusion layer pastes has a balance of both water repellency andbinding properties. By way of specific example, carbon paper (TGPH060H,product of Toray Industries, Inc.) serving as the substrate of thediffusion layers is immersed in a dispersion of FEP(tetrafluoroethylene-hexafluoropropylene copolymer), dried at 60° C. forone hour, and then subjected to heat treatment (FEP water repellenttreatment) at 380° C. for 15 minutes. The above procedure is performedsuch that the carbon paper to FEP weight ratio is 95:5 (for the cathode)and is 60:40 (for the anode). Hence, the carbon paper is uniformlysubjected to repellent treatment.

Next, carbon black (Vulcan XC72R, product of CABOT Corporation),terpineol (product of Kishida Chemical Co., Ltd.) serving as a solvent,and Triton (nonionic surfactant, product of Kishida Chemical Co., Ltd.)are uniformly mixed at room temperature for 60 minutes by means of amulti-purpose mixer (product of DALTON CO., LTD.). In this instance, themixing is performed such that the weight ratio of carbonblack:terpineol:Triton, is 20:150:3 in order to prepare the carbon pasterequired. A low molecular weight fluororesin (LUBRON LDW40E, product ofDAIKIN INDUSTRIES, Ltd.) is mixed with a high molecular weightfluororesin (PTFE30J, product of DuPont) such that the weight ratio ofthe fluororesins contained in the dispersion (low molecular weightfluororesin: high molecular weight fluororesin) is 20:3, therebypreparing the required cathode-use mixed fluororesin. The above carbonpaste is fed to a hybrid mixer container and cooled to 10 to 12° C. Theabove-described cathode-use mixed fluororesin is added to the cooledcarbon paste such that the weight ratio of carbon paste:cathode-usemixed fluororesin (fluororesin components contained in the dispersion),is 31:1. The mixture is mixed for 12 to 18 minutes using a hybrid mixer(EC500, product of KEYENCE CORPORATION) under a mixing mode. The mixingis terminated when the temperature of the paste reaches 50 to 55° C.,and the mixing time is adjusted accordingly as appropriate to achievethis temperature range. After the temperature of the paste reaches 50 to55° C., the mode of the hybrid mixer is switched from the mixing mode toa degassing mode, and degassing is performed for 1 to 3 minutes. Thepaste after degassing is allowed to self-cool, and the cathode-usediffusion layer paste is completed.

The above-described carbon paste and the low molecular weightfluororesin are fed into a hybrid mixer container such that the weightratio of carbon paste:low molecular fluororesin (the fluororesincomponents contained in the dispersion, and hereinafter referred to asan anode-use fluororesin), is 26:3. The mixture is mixed for 15 minutesusing a hybrid mixer under a mixing mode. After mixing, the mode of thehybrid mixer is switched from the mixing mode to a degassing mode, anddegassing is performed for 4 minutes. When a supernatant is present inthe upper portion of the paste after degassing, the supernatant isdiscarded. Then, the paste is allowed to self-cool, and the anode-usediffusion layer paste is completed. Each of the diffusion layer pastescooled to room temperature is applied to the surface of theabove-described carbon paper subjected to the FEP repellent treatmentsuch that a uniformly applied state is obtained on the surface of thecarbon paper. Then, the diffusion layer paste is dried at 60° C. for 60minutes by means of a hot air dryer (product of Thermal Co., Ltd).Finally, heat treatment is performed at 360° C. for 2 hours, and thediffusion layer is then complete.

A PtRu+WAu/C catalyst (Example 1) is employed at the anode 122. Thiscatalyst is prepared by evaporating gold (Au) compounds onto tungsten(W) to produce a WAu catalyst and adding the WAu catalyst to a PtRu/Ccatalyst (Pt:Ru=1:, product of Tanaka Kikinnzoku Kogyo K. K.). Morespecifically, the WAu catalyst is obtained by sublimating agold-acetylacetate complex under reduced pressure (1 Pa) to evaporategold onto the W and subjecting this to heat treatment at 250° C. for 4hours under an argon atmosphere. It has been known that, when theaverage diameter of the gold nanoparticles exceeds 10 nm, the COoxidizing ability decreases abruptly, and that, when the averagediameter of the gold nanoparticles falls within the range of about 1 to5 nm with the peak at 3 nm, outstanding CO oxidizing ability isexhibited.

Furthermore, when the mixing amount of Au with respect to the weight ofPtRu is 0.01 wt % or less, the effect of adding the gold nanoparticlesis not evident. When the mixing amount is 50 wt % or more, the catalyticfunction of converting H₂ to H⁺ is lowered, and working costs alsoincrease since gold has a low melting temperature and thus a difficultyarises in undertaking processes such as heat treatment. In view of thebalance between CO resistance and working cost, it is conceivable thatthe mixing amount of gold nanoparticles supported on the W with respectto the weight of PtRu is 10 to 40 wt %, desirably 5 to 10 wt %, and thatthe mixing amount in terms of the gold nanoparticles with respect to theweight of PtRu is 1 to 10 wt %, desirably 5±1 wt %. In the presentembodiment, the evaporation amount is adjusted at the time ofevaporation such that the mixing amount in terms of the goldnanoparticles is 5 wt % when the mixing amount of the gold nanoparticlessupported on the W is 13 wt %, and the WAu catalyst in which the goldnanoparticles, having a peak at a diameter of 3 nm, are supported by theW are mixed with PtRu/C.

In the case of the fuel cell 110 in which the anode 122 is contaminatedwith CO, as shown in FIG. 3, the reformed gas contains CO in an amountof several ppm, and this CO has a property that it is prone to stick tothe Pt serving as a catalyst. When CO sticks to Pt, the activity of thePt as a catalyst is lowered, and the anode 122 is brought into a stateof overvoltage (20 mV to 30 mV). Ru has a property of extracting, fromhumidifying water (H₂O) or the like supplied with the reformed gas, O orOH required for converting CO to CO₂, which does not affect catalysis.Thus, even when CO sticks to Pt, Ru located close to the CO can extractO or OH to thereby convert CO to CO₂. However, since theoxidation-reduction potential of Ru is high, the activation energy forthe conversion of CO to CO₂ cannot be reduced by Ru alone. When Au ispresent at this reaction site, the conversion of CO to CO₂ can bepromoted since Au has a property of reducing the activation energy forthe conversion of CO to CO₂.

Furthermore, when W is present in this reaction site, W exhibits aproperty of further promoting the function of Au which reduces theactivation energy for conversion of CO to CO₂, since W has theoxidation-reduction potential close to the oxidation reaction potential(0V) of the anode 122 (see p. 282 of Pourbaix). Therefore, according tothis example, when compared to a conventional PtRu/C catalyst, COpoisoning of Pt can be reduced, and the CO resistance of the anode 122can be improved. In addition to this, the durability of the fuel cell110 can be improved.

In Example 1, gold nanoparticles supported on W are added to PtRu/C. Itis sufficient that the catalyst for the anode 122 of the fuel cell 110contains: a material (a first catalyst material) having a function ofconverting a hydrogen source (H₂ in the first embodiment) to a proton(H⁺); a material (an oxygen-supplying material) having a function ofsupplying O (or OH) required for converting, to CO₂, CO which sticks tothe first catalyst material and lowers the ability thereof; and amaterial (a second catalyst material) having a function of reducing theactivation energy for the conversion of CO to CO₂ in order to facilitatethis conversion. Examples of the material which can be employed as theoxygen-supplying material include, in addition to Ru: transitionelements (transition metals) such as vanadium (V), chromium (Cr),manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu),zirconium (Zr), molybdenum (Mo), rhodium (Rh), palladium (Pd), tungsten(W), and iridium (Ir); magnesium (Mg); aluminum (Al); zinc (Zn); and tin(Sn).

Examples of the material which can be employed as the second catalystmaterial include, in addition to WAu, gold nanoparticles themselves,SnAu (gold nanoparticles supported on tin (Sn)), and CrAu (goldnanoparticles supported on chromium (Cr)). In particular, Sn has anoxidation-reduction potential close to the oxidation reaction potential(0V) of the anode 122 (see p. 479 of Pourbaix) and thus has a propertyof promoting the function of Au which reduces the activation energy ofthe conversion of CO to CO₂. Therefore, according to this Example, whencompared to a conventional PtRu/C catalyst, CO poisoning of Pt can bereduced, and the CO resistance of the anode 122 can be improved. Inaddition to this, the durability of the fuel cell 110 can be improved.

The fuel cell 110 of this embodiment is produced by employing the abovePtRu+WAu/C catalyst in the anode 122. More specifically, for producingthe anode 122, PtRu+WAu/C (carbon support, VULCAN XC72, product of CABOTCorporation) is mixed with an electrolyte solution (20% Nafion(registered trademark) solution) in a ratio of PtRu+WAu/C to electrolytesolution of 1:2 to thereby prepare the anode slurry. Next, this anodeslurry is applied to the surface of the packed layer 124 which is formedin the diffusion layer 128 by applying the anode-use diffusion layerpaste thereto, thereby producing the anode electrode. Furthermore, forproducing the cathode 114, Pt/C (carbon support, VULCAN XC72, product ofCABOT Corporation) is mixed with an electrolyte solution (20% Nafion(registered trademark) solution) in a ratio of Pt/C to electrolytesolution of 3:8 to thereby prepare the cathode slurry. Next, thiscathode slurry is applied to the surface of the packed layer 116 whichis formed in the diffusion layer 120 by applying the cathode-usediffusion layer paste thereto, thereby producing the cathode electrode.A solid electrolyte membrane (Nafion (registered trademark) 112) 112 isheld between the anode electrode and the cathode electrode and issubjected to hot pressing at about 140° C., thereby producing the fuelcell 110 (Example 1).

The fuel cell of Example 2 employs a PtRu+SnAu/C catalyst in the anode.This fuel cell is produced by the same production method as the methodused to produce the fuel cell 110 of Example 1, except that SnAu isemployed in place of WAu. Furthermore, as a Reference Example, a fuelcell is produced which employed PtRu+Au/C formed by evaporating gold(Au) compounds having a peak at a diameter of 3 nm onto a PtRu/Ccatalyst such that the amount of the gold nanoparticles is 5 wt % withrespect to the weight of PtRu. In addition to this, as a ComparativeExample, a fuel cell is produced which employs a conventional PtRu/Ccatalyst not containing the second catalyst material. FIG. 4 shows theresults (current-voltage curves) of current-voltage characteristicmeasurements by use of the fuel cell (a single cell) of Examples 1 and2, Reference Example, and Comparative Example. As can be seen in FIG. 4,in the fuel cells containing the second catalyst material, voltagereduction is small even when current density is increased, and thus astable voltage can be obtained over a wide current range. That is to saythat, even when a fuel cell is brought into a state in which thedeterioration of the fuel cell progresses rapidly as in a high loadstate, the fuel cell exhibits resistance thereto. Thus, it isconceivable that, by mixing the second catalyst material, the durabilityof a fuel cell is improved.

As another example, the following fuel cell can be envisaged. That is,as in Example 1, a WAu catalyst is produced by evaporating gold (Au)compounds onto W, and this WAu catalyst is then added to PtRu/C (productof Tanaka Kikinnzoku Kogyo K. K.) to produce a PtRu+WAu/C catalyst to beemployed. However, in this case, in contrast to Example 1, two differenttypes of PtRu/C, containing different Ru amounts, are employed. Morespecifically, a catalyst A is prepared by adding a WAu catalyst toPtRu/C having a Pt:Ru ratio of 1.4:0.6. In addition, a catalyst B isprepared by adding the WAu catalyst to PtRu/C having a Pt:Ru ratio of0.6:1.4 (Example 3).

The absolute amount of CO in the reformed gas supplied to the anode 122does not vary while the reformed gas flows from an inlet to an outlet.However, since the relative amount increases, the influence of COpoisoning is larger near the outlet of the reformed gas than near theinlet. More specifically, assuming that the ratio of components of thereformed gas near the inlet is 80% hydrogen, 20% carbon dioxide, and 10ppm carbon monoxide, and that the fuel cell 110 is operated at a fuelutilization ratio of 70%, then the ratio of the components near theoutlet is about 55% hydrogen, about 45% carbon dioxide, and about 23 ppmcarbon monoxide. Thus, the concentration of carbon monoxide near theoutlet is increased and is approximately two or more times of that atthe inlet. Hence, in Example 3, two types of catalysts are employed inwhich the Ru amount (relative amount) in one of the catalysts is twotimes or more of that in the other. According to Example 3, the COresistance of the anode 122 can be enhanced, and thus the durability ofthe fuel cell 110 can be improved as in Example 1. In addition to this,it is reasonable to assume that the anode 122 has uniform CO resistance.

The fuel cell 110 of this Example is produced by employing the above twotypes of catalysts at the anode 122 (FIG. 5). An electrolyte solution ismixed with each of catalyst A and catalyst B such that the ratio of thecatalyst and the electrolyte solution is 1:2, thereby producing an anodeslurry A and an anode slurry B. The anode electrode is produced asfollows. The anode slurry A is applied to the upper half of thediffusion layer 128 having the packed layer 124 formed by applying thediffusion layer paste thereto, the upper half being located near theinlet of the reformed gas. The anode slurry B is applied to the lowerhalf of the diffusion layer 128 having the packed layer 124 formed byapplying the diffusion layer paste thereto, the lower half being locatednear the outlet of the reformed gas. Furthermore, for producing thecathode 114, Pt/C is mixed with an electrolyte solution in a Pt/C toelectrolyte solution ratio of 3:8 to thereby prepare the cathode slurry.This cathode slurry is applied to the surface of the packed layer 116which is formed in the diffusion layer 120 by applying the cathode-usediffusion layer paste thereto, thereby producing the cathode electrode.The solid electrolyte membrane 112 is held between the anode electrodeand the cathode electrode and is subjected to hot pressing at about 140°C., thereby producing the fuel cell 110.

Second Embodiment

In this embodiment, with reference to FIG. 6, a description will begiven of a fuel cell 210 employed in a mobile-use fuel cell system 200.The fuel cell 210 is a direct methanol fuel cell (DMFC) in which anaqueous solution of methanol or pure methanol (hereinafter referred toas “methanol fuel”) is supplied to anodes 222 (222 a, 222 b, and 222 c).The fuel cell 210 includes a catalyst coated membrane (CCM) 230 servingas a power generation unit and which is formed by sandwiching a solidpolymer membrane 212 between cathodes 214 (214 a, 214 b, and 214 c) andthe anodes 222 without using a diffusion layer.

The methanol fuel to be supplied to the anodes 222 is supplied to a fuelchamber 254 from outside of the fuel cell 210 through a methanol fuelsupply hole (not shown). The methanol stored in the fuel chamber 254 issupplied to each of the anodes 222. At the anodes 222, the reaction ofmethanol occurs as indicated in the chemical equation (3). Furthermore,H⁺ moves to the cathodes 214 through the solid polymer membrane 212, andelectrical power is drawn. As is clear from the chemical equation (3),carbon dioxide is generated from the anodes 222 through this reaction.Thus, a gas-liquid separation filter 260 is placed between the fuelchamber 254 and a plurality of anode-side product discharge holes 258′,258″ provided in an anode-side enclosure 256 a of the mobile-use fuelcell system 200.

This gas-liquid separation filter 260 is a planar filter having fineholes which selectively pass gas components and do not pass liquidcomponents. A material having methanol (alcohol) resistance is suitableas the filter material. Furthermore, a lightweight material havingstiffness and corrosion resistance is suitable as the material for anenclosure 256 (the anode-side enclosure 256 a and a cathode-sideenclosure 256 c). Examples of a suitable material include a syntheticresin and metals such as an aluminum alloy, a titanium alloy, andstainless steel. Further to this, tempered glass or a skeleton resin mayalso be employed. As in the gas-liquid separation filter 260, theenclosure 256 has a portion contacting the methanol fuel. Thus,preferably, a composite material formed by applying a fluorine-basedsynthetic resin onto the above synthetic resin or metal is employed,particularly in the portion contacting the methanol fuel. Furthermore,reference numeral 262 indicates a support member 262 which forms thefuel chamber 254 and tightens the CCM 230. Preferably, a material thesame as that for the portion contacting the methanol fuel in theenclosure 256 is employed as the support member 262.

Air is supplied to the cathodes 214 through a plurality of cathode-sideproduct discharge holes 264. Oxygen in the air reacts with H⁺ arrivingat the cathodes 214 through the solid polymer membrane 212 to formproduct water. The cathode-side product discharge holes 264 supply airto the cathodes 214 and discharge product water from the cathodes 214.These cathode-side holes 264 are provided such that the total areathereof is almost the same as the total area of the anode-side productdischarge holes 258. However, the number of the cathode-side holes 264is larger than the number of the anode-side holes 258, and the diameterof the cathode-side holes 264 is smaller than that of the anode-sideholes 258. Moreover, the inner wall of the cathode-side productdischarge holes 264 and the surface of a portion of the cathode-sideenclosure 256 c which has these holes 264 provided therein are coatedwith a functional coating material containing a photocatalyst such astitanium oxide. The product water discharged from the cathodes 214 isprevented from dripping by provision of a large number of small holes.Furthermore, by coating the inner wall with the functional coatingmaterial, the product water spreads thinly over the surface of the innerwall without clogging the holes. Thus, the product water evaporation isfacilitated, and breeding of microorganisms or the like can beprevented.

Preferably, this functional coating material contains a metal such assilver, copper, or zinc in order for an organic material decompositionfunction and an antimicrobial function to be activated even when themobile-use fuel cell system 200 is not irradiated with light, such assunlight, containing a specific wavelength for activatingphotocatalysis. Furthermore, when a user of the mobile-use fuel cellsystem 200 touches the fuel cell system 200, organic materials mayadhere to the fuel cell system 200. When the entire surface of theenclosure 256 is coated with the functional coating material, anyadhered organic materials can decompose. In this manner, a soilresistant function or an antimicrobial function can be provided for themobile-use fuel cell system 200. In order to prevent the methanol fuelfrom flowing from the anodes 222 to the cathodes 214, O-rings 266 (ananode-side O-ring 266 a and a cathode-side O-ring 266 c) are placed soas to surround the CCM 230. In this embodiment, the O-rings 266 arecompressed by the cathode-side enclosure 256 c and the support member262 to prevent the methanol fuel from flowing from the anodes 222 to thecathodes 214 and to prevent oxygen from flowing into the anodes 222.Preferably, the O-rings 266 are made of a material having flexibilityand corrosion resistance.

A PtRu+CrAu/C catalyst (Example 4) is employed at the anode 222. Thiscatalyst is prepared by evaporating gold (Au) compounds onto Cr toproduce a CrAu catalyst and adding the CrAu catalyst to PtRu/C(Pt:Ru=1:1, product of Tanaka Kikinnzoku Kogyo K. K.). Morespecifically, the CrAu catalyst is obtained by sublimating agold-acetylacetate complex under reduced pressure (1 Pa) to evaporategold onto the Cr and subjecting this to heat treatment at 250° C. for 4hours under an argon atmosphere. Since the weight and dimensions of thegold nanoparticles are the same as those in Example 1, a descriptionthereof will be omitted. The difference of Example 4 from Example 1 isthat Cr is employed as the second catalyst material in Example 4. Incontrast to W, Cr does not have an oxidation-reduction potential around0V. Therefore, although Cr has poor ability to further improve thefunction of Au, which facilitates the conversion of CO to CO₂, Cr issuperior to W in its ability to draw O or OH from H₂O.

The fuel cell 210 of Example 4 is produced by employing the abovePtRu+CrAu/C catalyst at the anodes 222. More specifically, to producethe anodes 222, the PtRu+CrAu/C is mixed with an electrolyte solution ina ratio of PtRu+CrAu/C to electrolyte solution of 1:2 to thereby preparethe anode slurry. Next, this anode slurry is applied to one surface ofthe solid polymer membrane (Nafion 115, product of DuPont) 212.Furthermore, to produce the cathodes 214, Pt/C is mixed with anelectrolyte solution in a ratio of Pt/C to electrolyte solution of 3:8to thereby prepare the cathode slurry. Next, this cathode slurry isapplied to the other surface of the solid polymer membrane 212, therebyproducing the fuel cell 210.

As described above, Cr has an excellent oxygen supplying function whichis however not as good as that of Ru. Thus, in view of the cost of Ru,an example (Reference Example) can be envisaged in which the samematerial is employed for the oxygen-supplying material and the secondcatalyst material. More specifically, a PtCr+Au/C catalyst is employedin which gold nanoparticles are evaporated onto PtCr/C (Pt:Cr=1:1) (seeFIG. 7). The PtCr+Au/C catalyst is obtained by sublimating agold-acetylacetate complex under reduced pressure (1 Pa) to evaporategold compound onto the PtCr/C and subjecting this to heat treatment at250° C. for 4 hours under an argon atmosphere. When the supported amountof gold with respect to the weight of PtCr is 0.01 wt % or less, theeffect of supporting the gold nanoparticles is not evident. When thesupported amount of gold is 50 wt % or more, working costs increasesince gold has a low melting temperature and thus a difficulty arises inundertaking processes such as heat treatment. In view of the balancebetween CO resistance and cost, it is conceivable that the supportedamount of gold is 1 to 10 wt %, desirably 5±1 wt %. Therefore, goldnanoparticles having a peak at a diameter of 3 nm are evaporated ontothe PtCr/C such that the supported amount is adjusted to 5 wt % at thetime of evaporation. Since the method for producing the fuel cell 210 ofReference Example by use of the above PtCr+Au/C catalyst at the anodes222 is the same as that in Example 4, a description thereof will beomitted.

Moreover, two types of PtCr+Au/C having different Au amounts may beemployed in order to produce a difference in the Au amount between thefuel inlet and the fuel outlet, as in Example 3. More specifically,PtCr/C is employed as the catalyst A, and a PtCr+Au/C similar to that inExample 4 is employed as the catalyst B. As with other Examples, and inthe case of the DMFC, Pt black or PtRu black may be employed in place ofPt/C or PtRu/C. When Pt or PtRu not supported on C is utilized as acatalyst, the average particle size of the Pt black or the PtRu black is0.004 μm. Therefore, although W, Sn, or Cr may be supported on C so asto align with Pt or PtRu as in Examples 1 to 4 and Reference Example,the W onto which gold compounds are evaporated is supported on PtRublack (or Pt black) as shown in FIG. 8 (Example 6). In this case, amaterial for supporting a gold nanoparticle may be Sn or Cr.

Table 1 summarizes the proposed Examples.

TABLE 1 REFERENCE COMPONENT PRIMARY FUNCTION EXAMPLE 1 EXAMPLE 2 EXAMPLE3 EXAMPLE 4 EXAMPLE EXAMPLE 6 FIRST PROMOTING REACTION PLATINUM PLATINUMPLATINUM PLATINUM PLATINUM PLATINUM CATALYST OF CONVERTING (GRADIENT)MATERIAL HYDROGEN TO PROTON SECOND PROMOTING REACTION GOLD GOLD GOLDGOLD GOLD GOLD CATALYST OF CONVERTING MATERIAL CARBON MONOXIDE TO CARBONDIOXIDE OXYGEN- SUPPLYING OXYGEN FOR RUTHENIUM RUTHENIUM RUTHENIUMRUTHENIUM CHROMIUM RUTHENIUM SUPPLYING REACTION ON SECOND (GRADIENT)MATERIAL CATALYST MATERIAL FIRST SUPPORTING EACH AMORPHOUS AMORPHOUSAMORPHOUS AMORPHOUS AMORPHOUS SUPPORTING MATERIAL, EXCEPT FOR CARBONCARBON CARBON CARBON CARBON MATERIAL THE SECOND CATALYST MATERIALGIVING-RECEIVING ELECTRON TO-FROM FIRST CATALYST MATERIAL SECONDSUPPORTING SECOND TUNGSTEN TIN TUNGSTEN CHROMIUM CHROMIUM TUNGSTENSUPPORTING CATALYST MATERIAL MATERIAL REDUCING POTENTIAL OF REACTION ONSECOND CATALYST MATERIAL

It is conceivable that a transition element (transition metal) selectedfrom group 3 to group 11 of the periodic table (from group 3A to group7A, group 8, and group 1B) can be primarily employed as a secondsupporting material which supports gold nanoparticles, as shown inTable 1. Specific examples of the second supporting material includemagnesium (Mg), aluminum (Al), vanadium (V), chromium (Cr), manganese(Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn),zirconium (Zr), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), palladium(Pd), tin (Sn), tungsten (W), iridium (Ir), and oxides thereof.

These metals or metal oxides include a material which is unstable byitself. The thermal, chemical, and electrochemical stabilities can bemaintained by converting a part or all of such a material to a solidsolution alloy or carbide.

When the oxidation-reduction potential of the second supporting materialis located near the CO oxidizing potential at an anode (−0.1 V to 0.4V), the CO oxidizing activity of the second catalyst material can beimproved. Examples of such a material include W and Sn. Since W and Sneach have an oxidation-reduction potential near the CO oxidizingpotential at an anode, W and Sn are considered to be a particularlypreferred material for the second supporting material.

In the above embodiments, the description has been given of a fuel cellin which reformed gas containing residual CO is supplied to an anode anda liquid fuel direct supply type fuel cell in which CO is likely to begenerated during a reaction process on an anode side, but the presentinvention is not limited thereto.

1. A fuel cell comprising: an electrolyte layer; a first electrodeprovided on one surface of the electrolyte layer; and a second electrodeprovided on the other surface of the electrolyte layer, wherein areaction fluid to be supplied to the first electrode contains carbonmonoxide or carbon monoxide is generated from a reaction fluid havingbeen supplied to the first electrode, and wherein the first electrodecomprises: a first catalyst material which has a function of extractingan electron from the reaction fluid; a first support which iscarbon-based and supports the first catalyst material; a second catalystmaterial which has a function of reducing activation energy forconversion of the carbon monoxide to carbon dioxide; a second supportwhich supports the second catalyst material and is a material selectedfrom the group consisting of magnesium (Mg), aluminum (Al), vanadium(V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni),copper (Cu), zinc (Zn), zirconium (Zr), molybdenum (Mo), ruthenium (Ru),rhodium (Rh), palladium (Pd), tin (Sn), tungsten (W), iridium (Ir), anda substance obtained by converting part or all of the materials in thegroup to a solid solution alloy or carbide; and an oxygen-supplyingmaterial which is supported by the first support and supplies oxygen,wherein the second support is in contact with the first support.
 2. Thefuel cell according to claim 1, wherein the second catalyst materialcontains gold and a transition metal selected from group 3 to group 11.3. The fuel cell according to claim 2, wherein a particle diameterdistribution of the gold has a peak within a range of from 1 nm to 5 nm.4. The fuel cell according to claim 2, wherein the transition metal hasan oxidation-reduction potential within a range in which a standardelectrode potential thereof with respect to a standard hydrogenelectrode is between −0.25 V and 0.25 V, both inclusive.
 5. The fuelcell according to claim 3, wherein the transition metal has anoxidation-reduction potential within a range in which a standardelectrode potential thereof with respect to a standard hydrogenelectrode is between −0.25 V and 0.25 V, both inclusive.
 6. The fuelcell according to claim 1, wherein the oxygen-supplying materialcontains at least one selected from the group consisting of magnesium,aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper,zinc, zirconium, molybdenum, ruthenium, rhodium, palladium, tin,tungsten, and iridium.
 7. The fuel cell according to claim 2, whereinthe oxygen-supplying material contains at least one selected from thegroup consisting of magnesium, aluminum, vanadium, chromium, manganese,iron, cobalt, nickel, copper, zinc, zirconium, molybdenum, ruthenium,rhodium, palladium, tin, tungsten, and iridium.
 8. The fuel cellaccording to claim 3, wherein the oxygen-supplying material contains atleast one selected from the group consisting of magnesium, aluminum,vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc,zirconium, molybdenum, ruthenium, rhodium, palladium, tin, tungsten, andiridium.
 9. The fuel cell according to claim 4, wherein theoxygen-supplying material contains at least one selected from the groupconsisting of magnesium, aluminum, vanadium, chromium, manganese, iron,cobalt, nickel, copper, zinc, zirconium, molybdenum, ruthenium, rhodium,palladium, tin, tungsten, and iridium.
 10. The fuel cell according toclaim 1, wherein the second catalyst material is spaced apart from thefirst support.